Prior to applying a coating to a surface, it is generally necessary to prep the surface to ensure that the surface has the appropriate surface roughness. Prepping the surface is often accomplished using grit blasting (e.g. using cast iron shot or aluminum oxide) or by using an abrasive-entrained fluid. A variety of abrasives are known in the art, for example, sand, garnet, Zeolite (which are aluminosilicates of sodium, potassium, calcium or magnesium), alumina, and grit (i.e. crushed ferrous or synthetic abrasives). These abrasive particles (herein referred to as “blasting particles”) can be used to prep a surface, be it metallic or non-metallic, to a desired surface roughness.
Once the prepping of the surface is complete, coating material, which may be in the form of coating particles, is applied to the prepped surface. Coating particles can be applied using various techniques such as, for example, thermal spray coating (including combustion powder flame spray and High Velocity Oxy-Fuel), plasma spray, cold spray, etc.
Once the surface prepping is complete, the surface may need to be cleaned or washed, either by rinsing or other such method to remove the blasting particles that may remain on the surface to be coated. In many cases, this is accepted as satisfactory. However, there are many instances where the particles regularly used for blasting become embedded in the atomic matrix of the surface to be coated. This is highly undesirable as even a single foreign particle may adversely affect the micro-structural properties of the surface to be coated. For instance, when the surface is coated with the high-velocity oxy-fuel (HVOF) process using metallic particles such as tungsten, the coating particles will not adhere to the surface at the location where the foreign particle is embedded. Thus, the point where the particle resides may become a point of weakness of the surface, and in service may lead to unpredictable behaviour, including catastrophic failure.
An improvement on this conventional prepping process would thus be highly desirable.